The invention relates to a device for cut-off or demolition of a concrete part, comprising means for inserting at least one cut-off element equipped with an elemental recipient designed to receive a reactive agent of chemical or mechanical nature to cause cracking of the concrete part by expansion effect.
A cut-off device using reentrant means placed in position before the concrete casting operation is performed to create a series of channels in the mass of hardened concrete has already been proposed. The reactive agent is then inserted in the channels communicating with the different recipients. Implementation of such a reentrant process makes use of a removable cage having a plurality of vertical rigid bars. The reaction of the expansion agent causes an explosion of the concrete mass, which requires the exploded concrete blocks to be dismantled.
The object of the invention is to achieve a cut-off or demolition device of simple construction enabling the breaking zone of the part of a concrete structure to be demolished to be defined precisely, without affecting the mechanical strength of the rest of the structure.
The device according to the invention is characterized in that the recipient of each cut-off element is formed by a flask, made in particular of plastic material, having a flat closed base, and a lateral casing forming an acute angle with the base, said angle being comprised between 25xc2x0 and 60xc2x0 to generate expansion forces designed to cause fracturing of the concrete part along the breaking zone defined by the base, and a lifting movement of small amplitude of the concrete block after cut-off. The apex of the casing is fixed to a support means for placing the base at the required demolition level.
According to a preferred embodiment, the support means comprise a rigid tube joined to a tubular connecting spout arranged at the apex of the casing, said tube acting as inlet channel for insertion of the demolition agent into the flask.
Insertion of each cut-off element can be performed individually, or grouped by means of a positioning frame, before or after the concrete casting operation.
According to one feature of the invention, the positioning frame is fixed before the concrete casting operation to salient reinforcing bars by means of spacers spaced angularly between the different tubes of the cut-off elements. The spacers advantageously extend in the radial direction towards the inside of the positioning frame to confine an orifice for axial passage of the concrete casting pipe.
The flat base of the flask of each cut-off element is generally arranged horizontally and extending perpendicularly to the direction of insertion. This results in a horizontal fracture of the concrete along a plane passing through all the coplanar bases of the flasks. The block cut-off at the base then simply has to be lifted and the operation is finished.
It is also possible to obtain a diagonal fracture by using flasks with oblique bases arranged on the positioning frame in an inclined plane.
According to a development of the invention, each flask can be filled with a delayed-action expansive agent and is then placed in position before or after the concrete is cast, without making use of the filling tubes.